retroviral infection of lymphoblastoid cells

Hi All!
I am looking for some help with my retroviral infections. I have various
luciferase constructs which I have transfected into BING cells and have
frozen the virus stocks (at least I think I have virus--the BING cells showed
luciferase activity when they were assayed following the final viral
harvest). I am then attempting to infect two different lymphoblastoid
cell lines with these constructs, but with no success thus far. I have
tried all kinds of things including centrifugation at 2500rpm/32¡C,
phosphate depletion prior to infection, and/or simply adding the viral
sup to the cells. After selecting my cells for 3 weeks or more, I have
no luciferase activity. I know that these cells aren't the easiest to
infect, but this is getting ridiculous! Does anyone have a tried-and-true
protocol for infecting lymphoblastoid cells that you could share with
me? Also, what is the best way to change the media on these cells after
infecting them? Any and all suggestions would be greatly appreciated!
Thanks in advance
Kim Winkeler
Emory University
kwinkel at emory.edu